The present invention relates a dot matrix hologram with a hidden image, wherein a hidden image technology is applied to a dot matrix hologram.
In a conventional hologram, for reconstructing a hidden image, even the illuminating conditions of incident laser are unchanged, the reconstructed position of the hidden image shifts apparently when the illuminated area of the hidden image region changes. However, the present invention can overcome such problem.
In the present invention, a group of grating dots are formed as a basic block of grating dots. The shape of the basic block is rectangular. In general, it is designed that the lengths of sides of the rectangular shape are approximately equal to each another. Then the basic block of grating dots is two-dimensionally periodically repeated to from a group of blocks of grating dots with a matrix arrangement to constitute the hidden image region of a hologram. Since the corresponding grating dots in all of the blocks of grating dots are identical, and the grating dots with identical pitch and angle may diffract the convergent laser light to focus at a point behind the back side of the hologram (for a transmissive type hologram) or in front of the front surface of the hologram (for a reflective type hologram), therefore, the reconstructed position of the hidden image is independent on to the position of the illumination area of the hidden image region. Since all the grating dots in each block of grating dots are different, and every grating dot serves to diffract laser beam to a bright element dot of the hidden image, therefore, wherever the hidden image region is illuminated by laser light, the same hidden image can be generated by diffraction for each bright element dot in the hidden image having its corresponding grating dot in the block of grating dots and the grating in the block being two dimensionally duplicated to form a hidden image region. Besides, by controlling the diffractive efficiency of the respective grating dots in all blocks of grating dots, the reconstructed hidden image can be shown with independent brightness at all its bright element dots. It is necessary that the size of the block of grating dot is much smaller than the position difference of the bright element dots of the hidden image. When the maximum position difference of the grating dots in a block of grating dots is much smaller than the position difference of two adjacent bright element dots of the hidden image, the position exchange of the grating dots will not affect apparently the appearance of the reconstructed hidden image. Moreover, since the blocks of grating dots in the hidden image region are formed by two dimensional duplication, thus in a general illumination, it will present a matrix type of images with the same dynamic effects simultaneously.